Method of making corrugated paperboard

ABSTRACT

A method of manufacturing wax impregnated corrugated paperboard which includes the steps of moisture conditioning a first side of corrugating medium and impregnating the second side of the corrugating medium with wax prior to forming the corrugated paperboard.

United States Patent McDonald et a1. 1 1 July 1, 1975 [54] METHOD OF MAKING CORRUGATED 2,402,237 6/1946 Carder 156/583 X 2,443,222 6/1948 Bergstcin 117/158 X PAPERBOARD 2 659 680 11/1953 G 117/60 X ray 1 Inventors: WIlham McDonald; gh B. 2,967,116 1/1961 Hollinger 61 31.... 6 117/102 Johnson, both of Georgetown, S.C. 2,982,333 5/1961 Little 161/137 3,031,355 4/1962 Limerick el al. 156/549 X 1731 Asslgneei '"mmtmnal New 3,033,708 5/1962 McKee 161/235 x York, N.Y. 3,041,219 6/1962 Steck 1 161/127 X 3,146,121 8/1964 Turner 1 1 117/60 [22] mm July 1974 3,161,610 12/1964 Weisgerleret a1. 208/40 x [211 App] N6: 485,239 3,187,980 6 1965 085 et a1, 2 229 34 3,196,021 7/1965 0215 et 31..., 99/192 Related Application Data 3,308,006 3 1967 Kresse et a]. 1 5 116/235 x [63] Continuation of Ser. No. 165,360, July 22, 1971, 3 H1968 BOmaf 81 /1 abandoned, which is a continuation of Ser. No 7,419, Feb, 6, 1970, abandoned, which is a P E G F Le me COntiflUBIiOfl of S81. NO, 616,756, Feb. 13, 1967, r "1 eorge s S abandoned, which is a continuation-in-part of Ser. Asslsmm Exammerf\lan MCDOnaIq 475,736, 29, 1965 Attorney, Agent, or F1rmAlfred L. Mlchaelsen [52] US. CL. 156/210; 156/205; 156/208;

156/462; 156/470; 161/133; 161/137 1571 ABSTRACT CI. A method of manufacturing wax impregnated o ru, Fldd Search 156/205, 2061 2071 2081 gated paperboard which includes the steps of moisture 156/210, 462, 469, 470, 471, 472, 4 3; conditioning a first side of corrugating medium and 161/133, 134, 35, 137, 235 impregnatin the second side of the corru atin mei g C g g I R f C d drum w1th wax prior to formmg the corrugated paper- 56] eerences ite boani UNITED STATES PATENTS 1,796,542 3/1931 SChOO 156/205 x 13 3 Dmwmg WAX IMPREGNATED SINGLE-FACE!) IOO BOARD ADJUSTABLE PRESSURE, i SPRING LOADED RUBBER COVERED ROLL I 1c WAX IMPREGNATED 1.66 551% 19 ENGRAVED 20 Q 23 2 63 1351 01171116 WAX ROLL 24 HEATED ROLLS IMPREGNATED 22 PRESOSLLLRE 29 .I 3 MEDIUM MA 14 I2 10 a 1 I8 145 e H O Q 25 26 2a 1.111: TRANSFER ROLL A 0 l7 8 PREHEATER 27 o 0 GLUE PlCKUP ROLL WATER PRE-HEATING ROLLS 01.1112 PAN SPRAY Q '5 1 METHOD OF MAKING CORRUGATED PAPERBOARD This application is a continuation of application Ser. No. 165,360, filed July 22, 1971, now abandoned, which was a continuation of application Ser. No. 7,4 l 9, filed Feb. 6, 1970, now abandoned, which was a contin uation of application Ser. No. 616,756 filed Feb. 13, 1967, now abandoned, which was a continuation-inpart of application Ser. No. 475,786, filed July 29, 1965, now U.S. Pat. No. 3,366,496.

This invention relates to corrugated paperboard and, more particularly, to a method of making corrugated paperboard and to shipping containers and other products made of such paperboard.

Corrugated paperboard comes in various grades and types, including primarily single-faced and doublefaced corrugated paperboard, and double and triplewall corrugated paperboard.

Single-faced corrugated paperboard (commonly called single-faced board) is made by gluing a flat sheet of paperboard or linerboard to a sheet of corrugated material which has been passed through a single facer and formed into a series of arches. In this way, the corrugations are held firm and are prevented from stretching or flattening. Single-faced board provides a considerable amount of cushioning for any product wrapped in it and, although it is used principally for wrapping and for interior packing, it is also widely used as a decorative material in window and point of purchase displays. Glass articles and other fragile items are often enclosed in this board before being packed in a container. It is also used quite extensively by retail stores for wrapping merchandise for local delivery.

Double-faced corrugated paperboard (also known as double-faced board) usually consists of two flat outer sheets of paperboard or linerboard, sometimes called liners, combined with a single corrugated intermediate member of paperboard. Prior to corrugating, the intermediate member is called a corrugating medium and after corrugating such member is called a corrugated medium.

The arch-type construction gives strength and rigidity to the double-faced board and serves as a cushion for anything which comes in contact with it. The sheet may be scored and folded without materially lessening its strength.

The primary use for double-faced corrugated board is for shipping containers. Over 90 percent of all corrugated containers are manufactured from this type of board.

It is also used to make liners, pads, tubes, and partitions for the inner packing of glassware and other fragile articles which require protection. It has many other uses, such as, for wardrobe cabinets, merchandise display stands, toys, and freight car doors.

Double and triple-wall corrugated paperboard are used primarily to package heavier and more cumbersome products. Essentially, such boards are made in the same manner as single and double-faced boards but with multiple corrugated mediums and liners secured together in a manner similar to that just described.

Along with its many advantages, corrugated paperboard has the disadvantage of losing its strength under wet or humid conditions. Therefore, most corrugated shipping container applications in the past have been primarily limited to dry packaging situations. This, of

course, has greatly curtailed the areas of use for such containers and, in cases of severe wet conditions, for all practical purposes, eliminated their use completely.

For this reason, substantial segments of the produce and meat industries, among others, have made limited or no use of corrugated paperboard as a packaging material because of the high incident of wet and humid conditions in their packaging situations.

For example, produce, such as peaches, are picked in the summer and it is necessary to cool them as quickly as possible to remove field heat and to prevent spoilage. A known method for accomplishing this is hydrocooling"; that is, cooling by use of water.

In one form of hydrocooling employed in the peach industry, the peaches are packed, in bulk, in open-top containers and subjected to a cold water shower. The water circulates around the peaches to cool them and drains through openings in the containers and into a water collection trough where it is recirculated back into the cooling system. After the peaches are cooled sufficiently, the tops are placed on the containers, which are stacked one atop the other on pallets and placed in high humidity refrigeration rooms to await shipment.

Since moisture is known to adversely affect the strength of corrugated paperboard, it has been the general practice to use wooden containers or woodwirebound crates in packaging peaches under the conditions just described, in spite of their expense and attendant difficulties in handling.

It is, therefore, a principal object of this invention to provide a shipping container formed of corrugated paperboard which is capable of use in the packaging of perishable foods, such as meats and produce, under moist or humid conditions.

Another object of the present invention is to provide a corrugated shipping container for use in the packaging of perishable foods which have been hydrocooled prior to storage and shipment.

A further object of this invention is to provide a corrugated paperboard container having good stacking strength.

A further object is to provide a corrugated paperboard container capable of withstanding a cold water shower and the rigors of storage and shipment.

Another object is to provide a container formed of corrugated paperboard having high resistance to water.

Another object is to provide a shipping container which is made of corrugated paper and is simple in construction and economical to manufacture.

The present invention is also of particular significance in the shipment of meat, fish, produce, and poultry packed in ice. It has heretofore, been the general practice to ship this type of food, particularly poultry, in wirebound wooden crates, but such crates give rise to a number of problems, all of which the present invention helps to obviate or overcome.

Perhaps the prime concern of the shipper of fresh poultry by truck or rail from, for instance, Atlanta, Georgia to Chicago, Illinois is to avoid contamination leading to spoilage. Such contamination can come both from within and without the shipping container or package. Accordingly, it is desirable to get away from the slatted wood and wire crates now in use which allow water from ice melted in one crate, splinters, and foreign objects to flow or pass into another neighboring crate or one stacked below it and allow such foreign matter to gain entrance between the slats and cause contamination of the poultry. Additional contamination and spoilage can come from exposed poultry and parts which can, and often do, protrude through the slats.

Further, it is desirable to heighten the insulation provided by any iced, fresh poultry container or packaging; to maintain or improve its strength notwithstanding the assault made on it by the melting ice in which the poultry must be packed; and yet, to reduce packaging bulk and weight so as to make the most efficient use of available shipping space.

Again, elimination of the presence of wood, which splinters, and wires, which tear, is welcome both to the workmen handling fresh poultry containers and their ultimate recipients, as is adequate stacking strength in the container. And, in reverse order, the poultry distributor or a chain store manager has a major interest in being provided with a printable container, rather than a slatted wood and wire box where stapled or pasted labels are short-lived in the presence of ice, water, grease, and rough handling, so that the handler can be given explicit, printed, handling instructions and others can be informed or persuaded by an advertising message.

What has been specified above as desirable is achieved with the product of the method of the present invention, along with other objects which will become evident, from the following disclosure, to those skilled in the art. And, it is all accomplished by, broadly, a resort to corrugated paperboard made by the present method instead of wooden slats and wire and the like.

A further object is to provide a shipping container formed of corrugated paperboard for packaging poultry, produce, fish or meats in ice.

Of course, not all corrugated paperboard is suitable for the purpose here being considered. For, not all corrugated paperboard has the requisite printability and resistance to water, grease, and cold, or, in other words, the necessary high wet strength, wet rigidity, and resistance to facial penetration by water, water vapor, gases, grease and organic fluids commonly involved in the packaging of meat, product, and dairy products, such as those just described.

Thus, particular attention must be paid to the choice of components, i.e., liners and corrugating medium, which go into making the corrugated paperboard to be used in the present invention and to the choice of the additives, formative steps, and manufacturing conditions involved in its production. Without such attention the corrugated paperboard of this invention would not, for instance, retain or have the improved wet strength and rigidity, i.e., the high resistance to burst, tear, crush, tensile stresses under conditions of prolonged ice and water exposure or water immersion, which provided the basis of selection of one or more of its components.

A further and principal object of this invention is, therefore, to provide a method of making corrugated paperboard having greatly improved wet strength and good resistance to water exposure.

Other objects and advantages will become apparent from the following specification, claims and drawing of the invention in which:

FIGS. 1, 2, and 3 are sequential schematic drawings of the method of making the corrugated paperboard of this invention.

As has been previously stated, the specific corrugated paperboard used in the containers and the method of making such paperboard are of paramount importance in the practice of the invention. Specifically, the paperboard must be capable of use in an environment of severe atmospheric conditions of wetness and humidity, which normally would tend to deteriorate the paperboard.

Preferably, the liners are formed from premium qualilty wet-strength paperboard or linerboard, available commercially under the trademark WEATHERTEX" owned by the international Paper Company, and the corrugating medium is formed from premium quality wet-strength paperboard, available commercially under the trademarks WEATHERTEX and HYDRO- CHEM", both owned by International Paper Company. The liners and medium typically are treated with wetstrength resins and other chemical modifiers during the papermaking operation.

The corrugating medium is additionally treated with wax or a molten blend of waxes and thermoplastic resins or thermoplastic resins alone prior to corrugating, using appropriate temperatures and moisture treatment or treatments so as to obtain a corrugated medium capable of use in the packaging of foods under wet, moist, or humid conditions.

Referring to the drawings, the corrugating medium 1, in the form of a paperboard web, is fed from a suitable source such as a supply roll, not shown, around a guide roll 2 and past a water spray which moisture conditions the web by subjecting it to a water mist or spray.

The corrugating medium, thus properly conditioned, is then fed around a guide bar 3 and a guide roll 4 and into the nip of a pair of wax impregnating or wax applicator rolls 5 and 6, where the critical step of this invention of treating or impregnating the corrugating medium l with wax (prior to the step of corrugating of such medium) occurs.

The lower portion of the engraved applicator roll 5 is positioned in a trough 7 containing the wax or wax blend to be used to impregnate the corrugating medium. As it rotates, the roll 5 carries a supply of wax into the nip or crevice and hence onto the corrugating medium 1. A wicking action occurs as the wax is applied to the medium.

The applicator roll 6 is pressure spring loaded and is adjustable to regulate the amount of wax which is picked up by the corrugating medium I.

A typical wax blend which may be employed to impregnate the corrugating medium 1 could consist of a molten mixture of waxes and petroleum resins polymers and copolymers.

The wax blend is applied in amounts approximating 10 to 40 percent (preferably 25%) of the weight of the paperboard and typically is heated from 245 to 255F (preferably 250F) depending on the grade and type of paperboard used and blend composition. Beyond 30 percent the synergistic effect appears to diminish and the performance gained is not commensurate to the added cost.

The treated medium may immediately thereafter be subjected to further moisture and temperature conditioning by means of water mists, heaters, and steam applicators, all prior to being fed to the corrugating rolls.

Moisture and temperature conditioning are important to the treatment of the corrugating medium. It has been found that these treatments enlarge the interstices of the sheet making it more receptive to the proper adhesion penetration necessary for adequate bonding, as further will be explained. Further, an appropriate moisture content improves the forming characteristic of the medium thereby minimizing the types of malformation possible during corrugating, and it also permits the use of conventional water system adhesives, also further to be explained.

The wax impregnated corrugating medium is then fed directly into the corrugating equipment.

The corrugating medium 1 is fed into the corrugating machine (commonly called the corrugator) around a guide bar 8, a pair of guide rolls 9 and 10 and over a guide member 11. It then passes around an upper corrugating roll 12 and into the corrugating nip between the upper roll 12 and the lower corrugating roll 13.

In order to heat the impregnated corrugating medium 1 to the proper temperature so that when the corrugating rolls do their work and so that sufficient wax will be in a fluent condition to enable the corrugations to be properly formed without damage to the sheet, the rolls l2 and 13 are heated by live steam. Ordinarily, with corrugating rolls having a diameter of from 9 to l2 inches, and with a web speed of 300 feet per minute, a roll temperature of typically 340 to 350F has been found to be adequate.

The corrugating rolls l2 and 13 may be coated with a plastic consisting of a tetrafluoroethylene polymer to prevent their sticking to the corrugating medium during the corrugating operation. This is particularly desirable in practicing the method of this invention when the corrugating medium is treated with highly modified viscose type resins.

The corrugating rolls l2 and 13 corrugate the wax impregnated corrugating medium 1 to form the corrugated medium 1C.

The corrugated medium 1C is then combined with a linerboard 14 to form the single-faced wax impregnated corrugated paperboard 100 of this invention, in a manner further to be explained.

After the corrugating operation is completed, a suitable adhesive 15 is applied either to the crests or flutes of the corrugations at a first surface 1A of the corrugated medium lC or to a first or inner surface 14A of the single-face linerboard l4 and such linerboard 14 is pressed against the corrugated medium at the single facer and held in place until it is secured thereto to form single-faced corrugated board.

When the corrugated medium 1C comes out of the nip between the corrugating rolls l2 and 13, it continues to travel around the lower corrugating roll 13, and during the first part of such additional travel the adhesive 15 may be applied to the flutes or crests of the exposed corrugations or to the linerboard 14 by means of a conventional adhesive-applying arrangement which includes glue pan for containing the adhesive, a glue pickup roll 16 which dips into the adhesive 15 in the pan and a glue transfer roll 17 which contacts the pickup roll 16 and transfers the required amount of adhesive to the first surface 14A of linerboard 14 or to the crests at the first surface IA of the corrugated medium 1C.

As has been stated, in one of the key steps of this process the corrugating medium I is treated with moisture prior to being impregnated with wax. It is important to observe that l) the water mist is sprayed against the first surface 1A of the corrugating medium 1; (2) that the wax is then applied to the opposite second surface 18 of the corrugating medium 1; (3) that the corrugated medium 1 is then corrugated; and, (4) lastly, that the adhesive 15 is applied to the flutes or crests at the first surface 1A (i.e., the surface previously treated with moisture) of the corrugated medium 1C and before the wax has completely migrated through the corrugated medium. When the linerboard 14 is pressed tightly against the crests of the corrugated medium 1C to form the single-faced board 100, a far better glue bond is formed by following the above-described steps, primarily because of the water treatment of the first surface 1A and the fact that when the bond is beginning to form the wax has not come completely through the corrugated medium 1C to the first surface 1A because of such water treatment.

The adhesive mixture which is employed is of the aqueous type, starch or starch-resin combination.

It is possible to use conventional water system adhesives of this type because of the fact that the corrugating medium IC has been moisture conditioned in the manner just described.

The single-face linerboard 14, in the form of a web, is fed from a supply roll, not shown, and past a water spray which moisture conditions the web.

The linerboard 14 is then fed around two guide rolls l8 and 19 and into the nip of a pair of wax impregnating rolls 20 and 21 which wax impregnate the linerboard 14 in a manner similar to that of impregnating rolls 5 and 6. The roll 20 is positioned in a trough or pan 22 containing the wax or wax blend to be used to impregnate or treat the linerboard l4 and as roll 20 rotates it carries the wax into the nip between the rolls 20 and 21 and onto the outer surface 14B of the linerboard.

The wax applied to the linerboard is in molten form and typically at a temperature of between 250 and 270F and is applied in amounts of from 5 to 20 percent (preferably 10%) based upon the weight of the board and the blend composition and the end result desired.

The wax or wax blend used to treat the single-face linerboard should be of a refined quality suitable for use in contact with foods and it is applied with particular regard respecting its temperature and point of application so as to obtain liners capable of use in the packaging of foods under wet, moist, or humid conditions.

The wax treated single-face linerboard 14 is then fed around an adjustable guide roll 23, a preheater 24, an adjustable guide roll 25, a guide roll 26, two preheating rolls 27 and 28 and a heated pressure roll 29.

The heating rolls heat and maintain the linerboard 14 at a temperature sufficient to activate the adhesive.

As the linerboard 14 travels around the pressure roll 29 the transfer roll 17 transfers adhesive to the inner surface of such linerboard, or to the first surface 1A of the corrugated medium 1C, in a manner previously described, and immediately following this, as the linerboard 14 continues its travel around pressure roll 29, the pressure roll 29 presses the linerboard l4 tightly against the crests of the corrugated medium 1C, which is still supported on the lower corrugating roll 13 to form singlefaced corrugated paperboard 100.

Because of such support considerable pressure may be used in applying the linerboard. A pressure of 50 pounds per linear inch, or such pressure as is customary in the industry for applying single-face linerboard or liners may be employed. Any desired type or weight of linerboard may be employed.

The double-faced wax impregnated corrugated paperboard 200 of this invention is formed by combining the wax impregnated single-faced corrugated paperboard 100 with a double-faced linerboard in a manner further to be described. Such operation is accomplished at a double-facet or double backer.

The double-face linerboard 30, in the form of a web, is fed from a supply roll. not shown. past a moisture conditioning water spray. around a guide roll 31, into the nip formed by a pair of wax impregnating rolls 32 and 33 which operates to impregnate the outer surface 30A of the double-face linerboard 30 with wax from a pan 34 (typically at a 250 to 270'F temperature) in a manner identical to that described in connection with the single-face linerboard impregnating rolls and 21.

The wax impregnated double-face linerboard 30 is then fed around guide rolls 3! and 36, around a preheater 37, guide rolls 38 and 39, another pre-heater 40, a guide roll 41, and around a guide member 42 where it first comes into contact with the wax impregnated single-faced board 100.

The single-faced board 100 in the meantime is fed over a bridge (not shown) around pre-heater 43, a guide roll 44 and between an upper pressure roll 45 and a lower glue applicator roll 46 which applies adhesive from a pan 47, properly doctored by doctor roll 48. to the crests of the corrugated medium 1C.

The wax treated double-face linerboard 30 is pressed against the crests of the corrugated medium 1C to form the wax impregnated double-faced corrugated paperboard 200 of this invention.

The double-faced board 200 is then fed by a pull belt through a hot plate section. The heat and pressure provided by this section aid to form an effective glue bond.

in brief, a preferred method of making the wax impregnated double-faced corrugated paperboard of this invention comprises the steps of (l) impregnating a corrugating medium with wax or a wax blend prior to corrugating, (2) corrugating the corrugating medium to form a corrugated medium, and (3) securing the corrugated medium to first and second liners, to form double-faced corrugated paperboard. One of both of liners also may be treated with wax or a wax blend in separate operations.

The preferred method of applying the wax blend is inline-on the corrugetor thereby taking advantage of the heat generated by the corrugator. Wax continues to migrate during and after bonding'due to the heat of the corrugator.

The method of this invention has extremely important and novel advantage of being ableto impregnate the medium 1 and liners 14 and separately and with different formulations, blends. and quantities. Such flexibility is highly to be desired.

The invention may be employed on corrugating lines running at normal production rates of about 175 to 300 or 400 feet per minute. The non-standard weights of paperboard may be used but it is preferred to use 26, 38, 33 or 36 pounds per 1000 square feet for the corrugating medium and 26, 33, 38, 42, 4'7. 62. 69 or 90 pounds per 1000 square feet for the liners.

It has been found that the performance of the corrugated paperboard of this invention can be further improved by surface coating. preferably with hot melt wax blends. This is, of course. desirable in applications where external water is the primary hazard, such as in hydrocooling operations. The board is preferably printed prior to the surface coating operation but may be done afterwards also.

It may be preferred to wax the liners at one or more waxing stations after the belt. Typically, the first station consists of two driven and heated rolls and the second station of two driven rubber rolls. The advantage of positioning the rolls past the belt is that by so doing the belt is not exposed to wax and, therefore, there is no danger of wax build-up at high wax loadings.

The shipping containers of the present invention (not shown) are formed from blanks (not shown) formed from the wax impregnateddoubie-faced corrugated paperboard 206 of this invention. The orientation of the flutes of the corrugated medium is predominantly longltudinal of the blanks. The blanks may be formed from the corrugated paperboard 200 by well-known means and with standard equipment.

We claim:

1. The method of manufacturing wax impregnated single face corrugated paperboard which comprises:

a. continuously supplying a web of corrugating medium;

b. moisture conditioning a first side of said corrugating medium;

c. impregnating the second side of said corrugating medium with wax;

d. heating said impregnated corrugating medium;

e. corrugating said impregnated corrugating medium;

f. applying an adhesive to the crests of said impregnated corrugated medium, said adhesive being applied to the crests of said impregnated corrugated medium on said first side of said medium;

g. continuously supplying a web of single face linerboard;

h. heating said single face linerboard; and

i. securing said linerboard to said wax impregnated corrugated medium.

2. The method of claim 1 which further includes the steps of:

j. moisture conditioning the inner surface of said single face linerboard; and

k. wax impregnating the outer surface of said single face linerboard prior to heating said single face linerbnard.

3. The method of claim 1 wherein said medium is im' pregnated with a blend of wax and petroleum resin.

4. The method of claim 3 wherein said corrugated medium is 'Inpregnated with said blend in an amount between, approximately, 10 percent to 40 percent of the weight of said medium.

5. The method of claim 4 wherein said corrugated medium is impregnated with said blend in an amount between, approximately. 20 percent to 30 percent of the weight ofsaid medium.

6. The method of claim 5 wherein said moisture conditioning step comprises the step of spraying water on said first side of said medium.

7. The method of claim 2 wherein said single face linerboard is impregnated with wax in an amount from. approximately, 5 percent to 20 percent of the weight of said single face linerboard.

8. The method of claim 7 wherein said medium is impregnated with a blend of wax and petroleum resin.

9. The method of claim 8 wherein said corrugated medium is impregnated with said blend in an amount between, approximately, 10 percent to 40 percent of i. securing said linerboard to said wax impregnated the weight of said medium. corrugated medium;

10. The method of claim 9 wherein said corrugated j, ap lying n adhesive to the other crests of said immedium is impregnated with said blend in an amount pregnated corrugated di between, approximmely, 20 Percent to 30 Percem of k. continuously supplying a web of double face linerthe weight of said medium. board; and

The method of manufacmnng lmpreg'lated I. securing said double face linerboard to said corrudouble face corrugated paperboard which comprises: gated medium f suPPlYmg a web Of corrugating 12. The method of claim 11 which further includes b l t f t the steps of:

' mols um Con nonmg a e 0 Sal corruga in. moisture conditioning the inner surface of said ing medium;

c. impregnating the second side of said corrugating medium with wax;

d. heating said wax impregnated corrugating me- 15 single face linerboard; and n. wax impregnating the outer surface of said single face linerboard prior to heating said single face lindium erboard. e. corrugating said impregnated corrugating medium; th 't The neth0d of clam 12 whmh funher includes e 5 eps o f. applying an adhesive to the crests of said impregnated corrugated medium, Said adhesive being o. moisture conditioning the inner surface of said plied to the crests of said impregnated corrugated double face linerboard; and medium n aid fi id f id di p. wax impregnating the outer surface of said double g. continuously supplying a web of single face Iinerface linerboard prior to securing said double faCe board; linerboard to said medium. h. heating said single face linerboard;

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3 892 613 DATED 1 July 1, 1975 INVEN O I William S. McDonald et al tt rs certrtred that error appears \h the abovwrderrtrfted patent and that sarrl Letters Patent are hereby corrected as shown betow On the title page, part [63], after July 29, 1965 add "now U.S. patent No. 3,366,496".

Signed and Bealcd this twenty-third Day Of September 1975 [SEAL] A rresrt- C. MARSHALL DANN 

1. THE METHOD OF MANUFACTURING WAX IMPREGNATED SINGLE FACE CORRUGATED PAPERBOARD WHICH COMPRISES: A. CONTINUOUSLY SUPPLYING A WEB OF CORRUGATING MEDIUM, B. MOISTURE CONDITIONING A FIRST SIDE OF SAID CORRUGATING MEDIUM, C. IMPREGNATING THE SECOND SIDE OF SAID CORRUGATING MEDIUM WITH WAX, D. HEATING SAID IMPREGNATED CORRUGATING MEDIUM, E. CORRUGATING IMPREGNATED CORRUGATING MEDIUM, F. APPLYING AN ADHESIVE TO THE CRESTS OF SAID IMPREGNATED CORRUGATED MEDIUM, SAID ADHESIVE BEING APPLIED TO THE CRESTS OF SAID IMPREGNATED CORRUGATED MEDIUM ON SAID FIRST SIDE OF SAID MEDIUM,
 2. The method of claim 1 which further includes the steps of: j. moisture conditioning the inner surface of said single face linerboard; and k. wax impregnating the outer surface of said single face linerboard prior to heating said single face linerboard.
 3. The method of claim 1 wherein said medium is impregnated with a blend of wax and petroleum resin.
 4. The method of claim 3 wherein said corrugated medium is impregnated with said blend in an amount between, approximately, 10 percent to 40 percent of the weight of said medium.
 5. The method of claim 4 wherein said corrugated medium is impregnated with said blend in an amount between, approximately, 20 percent to 30 percent of the weight of said medium.
 6. The method of claim 5 wherein said moisture conditioning step comprises the steP of spraying water on said first side of said medium.
 7. The method of claim 2 wherein said single face linerboard is impregnated with wax in an amount from, approximately, 5 percent to 20 percent of the weight of said single face linerboard.
 8. The method of claim 7 wherein said medium is impregnated with a blend of wax and petroleum resin.
 9. The method of claim 8 wherein said corrugated medium is impregnated with said blend in an amount between, approximately, 10 percent to 40 percent of the weight of said medium.
 10. The method of claim 9 wherein said corrugated medium is impregnated with said blend in an amount between, approximately, 20 percent to 30 percent of the weight of said medium.
 11. The method of manufacturing wax impregnated double face corrugated paperboard which comprises: a. continuously supplying a web of corrugating medium; b. moisture conditioning a first side of said corrugating medium; c. impregnating the second side of said corrugating medium with wax; d. heating said wax impregnated corrugating medium; e. corrugating said impregnated corrugating medium; f. applying an adhesive to the crests of said impregnated corrugated medium, said adhesive being applied to the crests of said impregnated corrugated medium on said first side of said medium; g. continuously supplying a web of single face linerboard; h. heating said single face linerboard; i. securing said linerboard to said wax impregnated corrugated medium; j. applying an adhesive to the other crests of said impregnated corrugated medium; k. continuously supplying a web of double face linerboard; and l. securing said double face linerboard to said corrugated medium.
 12. The method of claim 11 which further includes the steps of: m. moisture conditioning the inner surface of said single face linerboard; and n. wax impregnating the outer surface of said single face linerboard prior to heating said single face linerboard.
 13. The method of claim 12 which further includes the steps of: o. moisture conditioning the inner surface of said double face linerboard; and p. wax impregnating the outer surface of said double face linerboard prior to securing said double face linerboard to said medium. 